In a number of industries, it is important to determine the thickness of a wet film applied to a surface in order to check the accuracy of a coating operation. For this purpose, instruments have been used which have been rather complex and expensive or have required a skilled operator to obtain satisfactory accuracy. As a result, there have been a number of efforts to overcome the difficulties that have been encountered with prior art instruments.
In this connection, the most accurate of the prior art film thickness instruments were designed for measuring a dry or hard film. Such instruments typically took the form of micrometers, electronic and magnetic devices, but the accuracy of e.g. micrometers has either been largely dependent upon the skill of the operator using the instrument or have simply not provided the desired accuracy over a range of interests or have otherwise failed to give reasonably direct readings of film thickness. In addition, because of the dependency upon the properties of the film coating, e.g., surface tension, prior art instruments are subject to considerable error.
In order to measure the thickness of a film, a variety of devices have been proposed. Among these are Euverard U.S. Pat. No. 2,507,592, Euverard U.S. Pat. No. 3,128,558, and Lake U.S. Pat. No. 3,019,645 which all utilize either a concave groove in a roller wherein the groove is of varying depths or a roller which has a variable radius in order to determine the depth of a wet film, and Eskijian U.S. Pat. No. 3,758,957 in which the tip of a male threaded shank is advanced until it is just touching upon an outer film surface wherein a gap between a calibrated gauge nut and a probe body can be measured as indicative of wet film thickness. In addition, Euverard U.S. Pat. No. 4,776,099 discloses yet another type of wet film thickness gauge.
While these prior art instruments address problems noted herein above, they still do not fully achieve relative simplicity and a reliable measurement technique. As a result, the present invention is directed to overcoming the foregoing problems and accomplishing the resulting objectives.